No, I think you misunderstood the post I responded to a bit.
In the case where the current password is captured on the password change, you have two plaintext values that aren't stored yet and you can just do some text analysis and understand how close they are.
With past passwords, you just take the current input and transform it with common transformations (adding numbers, incrementing/decrementing numbers, etc), hash it, and see if it matches a previous password hash. If so, then you know that they're using a very similar password pattern repeatedly.
In the case where the current password is captured on the password change, you have two plaintext values that aren't stored yet and you can just do some text analysis and understand how close they are.
With past passwords, you just take the current input and transform it with common transformations (adding numbers, incrementing/decrementing numbers, etc), hash it, and see if it matches a previous password hash. If so, then you know that they're using a very similar password pattern repeatedly.